In relevant technologies, a Long Term Evolution (LTE) network consists of evolved Node Bs (eNBs) in an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and an Evolved Packet Core (EPC). The LTE is characterized by that the network tends to be flat. Further, the E-UTRAN comprises a set of eNBs connected with the EPC through an interface S1, and the eNBs can be connected with each other through an interface X2. It is should be noted that S1 and X2 are logic interfaces, one EPC can manage one or more eNBs, one eNB can also be controlled by multiple EPCs, and one eNB can manage one or more cells.
An LTE-Advanced (LTE-A) system is the next generation evolution system of the is LTE system. The LTE-A system employs a carrier aggregation technology to expand the transmission bandwidth, and each aggregated carrier is called a component carrier; as shown in FIG. 1, it can be seen that the component carriers include component carrier #1, component carrier #2 and component carrier #3, wherein the one filled with oblique lines is component carrier #1, the one filled with grids is component carrier #2, the one filled with vertical lines is component carrier #3, each component carrier includes multiple sub-carriers, and a component carrier can be continuous or discontinuous on the spectrum, that is, the spacing between component carriers can be 0. A downlink transmission bandwidth of the LTE-A system is formed by aggregation of multiple downlink component carriers; an uplink transmission bandwidth may include only one uplink component carrier, also may be formed by aggregation of multiple uplink component carriers, that is, the uplink bandwidth and downlink bandwidth of the system may include different amounts of component carriers. Even if the amounts of the uplink component carriers and downlink component carriers of the system are the same, the amount of component carriers included in the downlink receiving bandwidth of a terminal may still be different from the amount of component carriers included in the uplink sending bandwidth of the terminal.
As shown in FIG. 2, the downlink transmission bandwidth includes five downlink component carriers, namely, component carrier #1 to component carrier #5; the uplink transmission bandwidth includes only two uplink component carriers, namely, component carrier 1 and component carrier 2; in FIG. 2, oblique lines represent synchronization channels, vertical lines represent broadcast channels of the downlink component carriers #1, #2 and #3, and grids represent broadcast channels of the downlink component carriers #4 and #5; furthermore, system information in the broadcast channels of the downlink component carriers #1, #2 and #3 includes a frequency point position and a bandwidth of uplink component carrier 1, and system information in the broadcast channels of downlink component carriers #4 and #5 includes a frequency point position and a bandwidth of uplink component carrier 2. In is relevant technologies, the phenomenon of unequal amount of uplink component carriers and downlink component carriers can be called as asymmetric carrier aggregation.
In the LTE system, when a User Equipment (UE) performs inter-cell handover, a source service cell notifies broadcast-relevant part information acquired from a target cell, dedicated resource information distributed for the user equipment by the target cell, information of uplink/downlink frequency point and bandwidth and the like of the target cell to the user equipment through a Handover Command.
For inter-Node B cell handover, a Transparent Container of a Handover Request sent to the target eNB from a source eNB includes configuration information of Access Server (AS), key, Radio Resource Management (RRM) and the like, while a Transparent Container of a Handover Request Acknowledge message includes the broadcast-relevant part information of the target cell, the dedicated resource information distributed for the user equipment by the target cell, the information of uplink/downlink frequency point and bandwidth and the like of the target cell; since LTE system is a single-carrier system, the Transparent Container includes only one pair of uplink and downlink single frequency point information of the target cell, and if this information is default, it is deemed that all frequency point information of the target cell are the same as that of the current cell. For the handover in the LTE system, typically a non-contention based random access procedure is employed, comprising the following processing:
Step 1: notifying the dedicated random access resources for handover to the user equipment through the Handover Command, wherein the dedicated random access resources include a designated Random Access Channel (RACH) and a designated random access preamble, and sending the designated random access preamble, namely, a random access request, by the user equipment on the random access channel designated by the target cell;
Step 2: sending a random access response on the downlink by the target cell after the target cell receives the random access preamble sent from the user equipment; and
Step 3: receiving the random access response sent from the target cell in a designated search window, finishing the random access process, and further finishing is the handover by the user equipment after the user equipment sends the preamble.
However, in a multi-carrier LTE-A system, both the uplink bandwidth and downlink bandwidth can include frequency point information of multiple component carriers, and the frequency point information of all component carriers of the target cell will be transmitted to the user equipment through the Handover Command; however, when the target cell includes multiple uplink frequency points and there are random access resources on all multiple frequency points, the user equipment is unable to determine which frequency point should be used for initiating the random access request, and if there is no special agreement between the user equipment and the eNB, problems such as waste of random access resources or conflict of random accesses may be caused.